need help with usb device driver...

I'm trying to write a userland webcam device driver for dragonfly and I need
to open the device endpoint. The camera im using supports isochronus
transfers which would be endpoint 1 so the devicename should
be /dev/ugen0.1 in my case. Problem is when i try to open this file using a
open("/dev/ugen0.1", O_RDONLY) i get an invalid argument error... if i use
O_RDWR i get a device not configured erorr.
I have been able to retrieve all the basic descriptors using the control
endpoint (by opening "/dev/ugen0") but haven't been successful with opening
any other endpoints. I have looked at several other driver projects in
linux and freebsd and I'm not sure where to go from here.
thanks
-John